Landscape evolution of Punta Arena sand spit (SE Baja California Peninsula, NW Mexico): Implications of ENSO on landscape erosion rates

Abstract Coastal bars are deltaic landforms resulting from sediment mobilization from source to sink. The formation, evolution and extinction of coastal bars is of broad interest for Quaternary studies because these are natural archives of former and present climatic conditions where complex ecological and biological relations take place. The Pacific coast of Mexico contains many coastal bars, like the strand-plain of Nayarit (~1400 km2) which is one of the largest around the world. We present the first ages of the largest sand spit (~8.5 km2) of the SE part of Baja California Peninsula, named Punta Arena. OSL ages indicate that the innermost bar is 0.26 ± 0.02 ka (1755 ± 20 AD). Using OSL ages and data obtained from Landsat images we estimate a mean sedimentation rate of ca. 7.7 m yr –1. Results from satellite images spanning for 32 years (1984 to 2016) confirms that sand spit is accreting at ca. 0.6 m yr –1 along the bar formation zone and to ca. 0.7 m yr –1 along the longshore drift zone, such rates however, are significantly lower compared other formation periods between 1755 and 1984 CE when sedimentation rates were ~ 8 to ~ 52 m yr –1. The progradation of the sand spit is consistent with the apparent development and density of vegetation which dramatically drops from inland towards the coast. The analysis of rainfall data spanning from 1950 to 2015 indicates that the largest periods of sedimentation along the sand spit are related with extended non-rainfall months occurring during ENSO conditions. Our data indicate that climate in SE Baja California Peninsula has remained more or less stable since the LIA and the periods of landscape erosion, leading to the formation of bars and sand spit accretion, mainly occur under the warm phase of ENSO (La Nina) which produces extended periods of landscape dryness and intense rainfalls during the winter.